So here is an unfortunate but potentially valid scenario (numbers taken from https://gpuweb.github.io/gpuweb/#gpulimits).

Implementation on Metal has to support at least 4 bind groups. Each will take a slot in the vertex buffer table as an argument buffer, assuming they are supported. If they aren't... this gets much worse.

It has to support at least 8 dynamic uniform buffers and 4 dynamic storage buffers. How are the offsets passed? We were planning on just excluding the dynamic resources from the argument buffer and binding them separately. That would mean at least 12 more bindings taken.

Internally, it may need to bind a buffer with some extra data, say containing the size limits for out-of-bounds checking in the shader. That's one more buffer.

So what we end up is 17 buffers taken by non-vertex-attributes, and only 14 left for the vertex buffers for attributes, at most. Which means, an example implementation can't expose the base limit of 16 that is suggested above. A more complicated implementation could possibly put all the internal things together with dynamic offsets in a single buffer, but the feasibility of this path is yet to be considered in depth (and definitely needs to be discussed).

Another problem is that, if an implementation wants to report a higher limit for any of these, it can't do so for all the limits. I.e. supposing it has an extra buffer. It could either report it as a max bind groups limit of 5, or as a max dynamic storage buffer limit as 5, but not both, and hence - will not be able to run applications that it should be able to run.

I wonder if we can look at it together with #684 and say that:

an implementation may fail to request a device with multiple limits that are above the baseline

That would be totally matching this case here with vertex attributes, and it would discourage users to just blindly request all the limits.

Figure out the base vertex input limits #693

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